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Think you have Nicole Richie to thank for starting the oversized sunglasses trend? It was actually former First Lady Jacqueline Onassis, who also helped popularize colorful sheath dresses, slim-fit jeans and Manolo Blahniks. To mark what would have been her 80th birthday, The Huffington Post is taking a look back at Jackie’s post-Camelot style. Follow our coverage of the current First Lady‘s cutting edge style and you’ll see why many are referring to her as Michelle O.

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I’ve been suffering through 57-minute-long full body workouts alongside Kelly Ripa and Elle Macpherson for over a year at Physique 57′s Manhattan studios and in turn my butt looks lifted, my arms feel toned and I can do 10 real push-ups! Founders Tanya Becker and Jennifer Vaughan Maanavi created the groundbreaking cardiovascular program made up of isometric exercises and orthopedic stretches and they just released three at-home videos— More

While promoting her new film, Sienna Miller has been forgoing the usual red carpet uniform of fussy gowns in favor of dressy pant ensembles. The G.I. Joe star looked undeniably fierce at the movie’s Japanese premiere last night in a shimmery, skintight Gucci pantsuit. The next time your invite calls for cocktail attire, take a page from Sienna’s style book: give your LBD a rest and pair dressy pants with a silk blouse and bold earrings.

Pants, Siwy, $228; visit chickdowntown.com.

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Last we spoke to Estelle, she wanted to start a shoe line called “C’est Moi.” Now, the singer is one step closer to adding “fashion designer” to her resume. Today Rachel Roy announced that she plans to collaborate with Estelle on a jewelry line. The designer announced on her Twitter account, “I am excited to work with Estelle on a jewelry collection, which will debut in spring 2010.” The range is still in development, but if their tastes are any indication, we can expect head-turning statement earrings.

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Waiting to find out if you’ve won a walk-on role on Season 4 of Mad Men? See what you’d look like mingling with the cast of characters at the Sterling Cooper Advertising Agency right now with AMC’s new Mad Men Yourself tool. Choose a body type, recreate your facial features and style your wardrobe (martinis count as accessories, naturally) then put yourself in the picture. Among the scenarios: have coffee in Betty’s kitchen or flirt with Don in a dark bar. Download your favorite to use as a screensaver or share your creation with friends on Facebook or Twitter.

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